Block cave mining is a method of mining that is gaining popularity, despite the fact that it has been in use for some years. One of the factors that hinders the advancement of block cave mining technology, however, is that it is difficult to determine what is happening inside the rock mass during the mining process. Some theories state that comminution may occur within the rock mass, although there continues to be little known about the rock dynamics with any degree of certainty.
A precise understanding of the actual flow of the ore body during the mining process would be advantageous, to ensure that current practices and knowledge about the block cave mining method are as efficient and complete as possible and to ensure that beneficial changes to operating techniques can be developed. Determining the rock breakage characteristics is of paramount importance to placing drawbells and accurately controlling the pull of the ore. More specifically, the ore body dynamics are important for a determination of the number of draw points required during mining, determination of the exact location of the cave front on a daily basis, the potential to alter tipping practices to use the contained energy in the ore body for enhanced comminution, and the safety of the miners based on knowledge of the cave front location and behaviour. Gathering rock flow information is difficult as the cave, once started, is completely independent inside the rock mass. Only gross controls, such as drawbell pulling, can be used to attempt to change the pull characteristics, but typically results are apparent significantly after the fact and correlation with changes are difficult to measure.
Several attempts have been made to determine what is occurring within the rock mass during the mining process. Generally, these attempts have taken the form of either markers or computer simulations.
Markers have been injected into the rock mass to try to determine the material flow characteristics. The markers have typically been made of steel and injected into the rock mass above the ore body. As the ore body starts to fracture, these markers begin to travel through to the rock mass to the draw bells below. These markers are collected and matched to entrance location and exit location. It is then assumed that the route of travel is a straight line between the two points representing the trajectory and thus the flow of the rock mass. Although some success has been achieved using this technique, the number and validity of assumptions underlying the technique and the lack of data due to loss of markers has resulted in limited effectiveness.
Computer software has also been used to simulate the flow of rock and several different simulation software systems exist. Some represent the rock as spheres while others use more rock-like shapes. The results of the computer simulations suggest that spherical rocks may be less able to represent reality than more realistic shapes. However, both of these methods suffer from a lack of empirical data and are of limited use.
There is no comprehensive measurement data from within the rock mass, or any other fluid mass, to gather real time information about the dynamics of the mass movement. In many cases, for example in mining, this is generally due to the physical constraints of entering the ore body with active sensing systems. For instance, sensors must be built so as to survive within the ore body, despite the high pressure and flow constraints. The sensing system must be robust enough to allow positioning within the ore body with sufficient accuracy that assumptions can be minimized. Such sensors must have a power system capable of lasting long periods of time while in the rock mass. The transmission system used must be capable of penetrating substantial thicknesses of rock of varying density in order to transmit and receive from the sensors. Also, an interface must be available for real time data analysis in order for the technical and operating personnel in the subsurface to determine information about the cave front.
A better understanding of the ore body flow would be beneficial to a number of aspects of the mining process. For instance, this information would be useful for the development of active mining control tools to control mining equipment. With a positioning system that can function within a rock mass, it would also be possible to develop a trapped miner rescue system based on the data through the use of an underground positioning system or “UPS.” The UPS would enable the movement of each miner to be tracked so, in a catastrophic event, the location of each miner can be accurately determined making rescue operations more efficient. In addition, mine-wide asset management systems could be developed in order to improve efficiency of mining operations.